Faulty map-controlled thermostat (heating element open or shorted).; Damaged or corroded wiring harness to the thermostat.; Loose or corroded connector at the thermostat.; Short to ground in the control circuit.; Failed engine control module (DME) driver, though rare.

DTC codes / BMW codes / P1619

P1619 · BMWMAP Cooling Control Circuit Signal Low

Q: What does code P1619 mean?

MAP Cooling Control Circuit Signal Low. P1619 on BMW vehicles indicates that the engine control module (DME) has detected a low signal on the control circuit for the map-controlled cooling thermostat. This thermostat uses a heating element controlled by the DME to regulate engine temperature, and a low signal means the circuit is likely shorted to ground or has excessive resistance, preventing proper thermostat operation.

P1619 on BMW vehicles indicates that the engine control module (DME) has detected a low signal on the control circuit for the map-controlled cooling thermostat. This thermostat uses a heating element controlled by the DME to regulate engine temperature, and a low signal means the circuit is likely shorted to ground or has excessive resistance, preventing proper thermostat operation.

SystemPowertrain

Code typeBMW specific

SeverityMedium

Fix difficultyIntermediate

AreaComputer and output circuits

Symptoms you may notice

Check Engine Light (CEL) illuminated on the dashboard.
Often no symptoms besides the warning light, especially in mild weather.
Engine may run cooler than normal or take longer to reach operating temperature.
Poor heater performance in cold weather due to low coolant temperature.
Increased fuel consumption as the engine runs rich when cold.
Possible overheating if the thermostat fails to open, though less common with a low signal.

Common causes, most likely first

Faulty map-controlled thermostat (heating element open or shorted).
Damaged or corroded wiring harness to the thermostat.
Loose or corroded connector at the thermostat.
Short to ground in the control circuit.
Failed engine control module (DME) driver, though rare.

How to diagnose and fix it

Scan all modules for fault codes and verify P1619 is current; clear and retest if stored.
Visually inspect the thermostat connector and wiring for damage, corrosion, or loose pins.
Measure resistance of the thermostat heating element and compare to BMW specifications.
Check for short to ground in the control wire between the DME and thermostat.
If wiring and element test good, test the DME output signal with an oscilloscope or bidirectional scan tool.
Replace the map-controlled thermostat if faulty, clear codes, and verify repair with a test drive.

Don't overlook the thermostat wiring

A low signal code often results from a short to ground in the wiring, not a failed thermostat, so always check the harness before replacing parts.
The map-controlled thermostat may fail intermittently, setting the code only under certain temperature conditions; a thorough wiggle test of the harness can reveal intermittent faults.
Some aftermarket thermostats have different resistance values and can trigger P1619 even when new; use OEM-quality parts.
The DME may set P1619 in conjunction with other cooling system codes; diagnose all codes together to avoid misdiagnosis.
A weak battery or charging system issue can cause spurious low-signal codes; verify battery voltage and ground connections.

Can I keep driving with P1619?

You can usually continue driving with this code, but monitor engine temperature closely and avoid heavy loads or long trips until repaired. If the engine overheats or the heater stops working, stop driving and seek service immediately.

Tools that help

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Guidance is general and written for BMW vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.